The man page for sshd has a section on the authorized_keys format, where it states that the comment extends to the end of the line. While I haven't tried it, you should be able to put spaces into the comment.

I've tried it and we will see if it works. My university requires ssh based login for some things and they said they use the comment (which must contain my username) matching an account to a key. Since I didn't wanted to create another SSH key I simply copied my public key, changed the comment and gave it to them. We will see if it works.
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MartinOct 29 '12 at 13:26